I bought a new pair of Frog Togg Amphibians last night. 1200 grams. I know they are not at all what your wanting, but they are by far the warmest boots I have ever put on. I tromped after coyotes all day today in 18 degree 30 MPH wind and my feet were on fire, and they are always cold.

Like I said, its not apples to apples but I thought this was a good place to brag about them.

Go with a CDN manufacturer. Kamik Helsinki model has great features and with its multi-layer liners, they are rated for -74C/-100F.

If it gets colder than -100F, I would stay indoors. Sorel makes a similar model. Minimum 2 layers of socks. First must be polypropolyene (wicking) and 2nd should be a wool/fleece type. Nice and loose. Boot should be a bit big to keep heat in the best.